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Old 06-12-2021, 10:50 PM   #31 (permalink)
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Old 06-13-2021, 01:55 PM   #32 (permalink)
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Okay wow, I managed to retard the intake cam successfully and also think I know how the DFCO works (I believe it's using idle speed as a starting point), this is a pleasant surprise. I decided to avoid modifying any non-integer value thinking there might be some checksum or some kind of other black magic being done with those values, and voila the ECU seemed happy. Going to try pushing my luck and change the cam position a little more. I have DFCO all the way to 1100rpm now, though it sometimes doesn't turn on when I downshift into 1st.

I think I am going back up a little on idle speed to 688rpm because the engine sputtered a few times with a 672rpm target idle after blipping the throttle. There's about a 1/5 chance that the engine tries to catch the idle and it dips below 590rpm, at which point it kind of coughs and sputters. On my old Scion FR-S, I had a pretty bad slow idle that I decided I would live with to save fuel, but this car being expensive to fix makes me nervous if it's doing stuff like that. As long as it's over 600rpm the engine runs very smooth, which is surprising given the huge cams.

Next step is adding some external EGR, and then getting the oil changed. When the engine is idling, I see an extra 0.1gph usage if the oil is cold!

Last edited by serialk11r; 06-13-2021 at 02:34 PM..
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Old 06-13-2021, 04:00 PM   #33 (permalink)
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Quote:
Originally Posted by serialk11r View Post
Next step is adding some external EGR
What do you expect from an external EGR on this engine? Are you considering a cooled or a warm EGR?
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Old 06-13-2021, 05:18 PM   #34 (permalink)
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What do you expect from an external EGR on this engine? Are you considering a cooled or a warm EGR?
It has hot external EGR already built in, it just looks underutilized to me, mostly relying on cam overlap to get internal EGR. Cam retard = less internal EGR and also less volumetric efficiency, add external EGR adds back the charge dilution with less pumping loss, and also adds timing to make up for the lower dynamic compression ratio and charge density.

The valve isn't very big, but at low load it can supply much more EGR than it does right now.
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Old 06-14-2021, 05:29 PM   #35 (permalink)
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Wow, I took it on the freeway to get some cheap Costco gasoline today and the dash indicated 25.5mpg@65mph in cruise control! That's a huge improvement over 23.0mpg stock. I had tape over the oil cooler in a slight different position so it blocks a little more of it off, but the oil definitely could not have been much above 100C because the freeway was a very short distance away and I immediately turned on cruise control to check the mpg gauge.

I think my intake cam retard must be responsible for most of it. I believe the cam should be something like 10-12 degrees retarded from its stock position, which should be in the vicinity of 5% reduction in volumetric efficiency, while internal EGR according to my simplistic modeling (residual exhaust gas + overlap * constant / rpm) should be down something on the order of 2%, so pumping losses are probably unchanged (EGR heats up the air) while combustion efficiency is up for one reason or another. It could be due to the fact that ignition timing appears unaffected by VVT, and now I have a faster burning mixture with the same ignition timing.

This kind of exceeded my expectations. 26mpg is probably within reach if I add a little more tape to the grille, 27mpg may be within reach with some external EGR, and 28mpg could be possible with thinner oil, which is honestly pretty respectable...a lot of V6 cars can't do much better.

I also realized that I could get mildly warm air if I do airbox and intake snorkel deletes (planned for when the air filters need replacement) and then tape off the entire bottom of the grille, as the engine would suck warmed air through the front bottom of the radiator from inside the engine bay. It would only be barely warm but it probably counts for something on a long trip and only needs a few strips of tape.
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Old 06-14-2021, 06:46 PM   #36 (permalink)
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25.5mpg@65mph in cruise control! That's a huge improvement over 23.0mpg stock.
That's in the vicinity of 10%. A good inducement to want to do more.
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Old 06-17-2021, 06:11 PM   #37 (permalink)
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Quote:
Originally Posted by serialk11r View Post
I also realized that I could get mildly warm air if I do airbox and intake snorkel deletes (planned for when the air filters need replacement) and then tape off the entire bottom of the grille, as the engine would suck warmed air through the front bottom of the radiator from inside the engine bay. It would only be barely warm but it probably counts for something on a long trip and only needs a few strips of tape.
Makes me wonder to which extent a warmer intake temperature could compensate for the lower EGR flow.
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Old 06-17-2021, 07:45 PM   #38 (permalink)
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I took the car out with even more intake cam retard and saw a lower mpg number, and then I remembered that 101 on the Peninsula has a very very slight uphill grade to San Francisco (I usually get something like 2-5% more mpg going south vs north), so I did a bit of a longer test run in both directions. It seems I averaged about 26mpg going south and 24mpg going north, so I cannot definitively say if I've actually gained any mpg yet, as the higher air temperature today could easily have caused the difference, or differences in oil temp, etc.

However when I add in a few % more EGR, hopefully I get more mpg. I'm starting with 1.5-2% over stock, then I may add a little more if it looks like the EGR valve can support more flow. Assuming I have around 1.5 bar FMEP including throttle loss, I should see about a 1% increase in fuel economy from reduced pumping loss.

The biggest difference is definitely going to come from using lighter engine oil. I am still a little paranoid about dropping the viscosity too much, but I need to keep reminding myself that the factory recommended fill is Castrol which is comparatively thin (4.1cP for 5W50, 5.2cP for 10W60), and it's meant for a 10000 mile OCI. Using Mobil1 10w-40 at 3.9cP HTHS with an OCI of more like 4000 miles *should* be okay, if Castrol 5W-50 is fine.

Last edited by serialk11r; 06-17-2021 at 07:52 PM..
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Old 06-19-2021, 12:35 AM   #39 (permalink)
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Well this is a fail, I successfully got the EGR valve to open up more but I needed quite a bit more load to maintain 60mph today compared to yesterday. The problem with this car is that it cools the oil with ambient air, has short gearing and a massive gearbox made for V12 cars so the friction forces completely dominate.

I have no idea if my bad mpg today is because the fluids were a little colder, if the ECU isn't adding spark timing, or if I'm actually losing engine efficiency with my tweaks. I want to say I probably lost engine efficiency because the difference seems significant, but I really have no idea...

I think I need to add more EGR to see if the engine is actually advancing the spark timing, because if it's not then that would easily explain the loss in efficiency. For now I've only added around 2% more EGR which is kind of negligible, whereas if I get closer to 5% it should show up.
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Old 06-19-2021, 12:46 AM   #40 (permalink)
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Maybe the engine is using more fuel to compensate for the higher temperature resulting in the increased EGR flow.

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